The Hoses at the Tank can be replaced with 5/16" ID Hose as well as the 2 sections of the Fuel Inlet Hose from the Fender Well to the Fuel Supply Pump.
Fuel Injection Hose SAE J30R9 or 30R90 SAE 30R9 that you can get a regular Auto Parts Store is lined with Viton; to Goodyear version has a Blue lining and there is also a Gates Version. Some where around $6 a foot.
On the Hose that attaches to the Fuel Tank Screen you need to file or grind off the crimped Collar and remove it. That leave you with a Hose Barb that you can use any Hose on.
The Cigar Hose does not seem to be prone to leaking as like the Other Hoses. However, that could be replaced with the 5/16" ID Hose. But, if it the Pulsation of the Hose makes noise you will need to revert back to the Cigar Hose.
For the Injector Return Lines you will need to find one of the threads if you want Viton. Some Member said some Hose is thinner than others.
Some People have used Plasti Weed Wacker Fuel Hose from a Lawn Mower Repair Shops: Injector return hose plastic tube
any lawnmower/chainsaw repair shop should have hose that will work too.
I bought a 50' box of 1/8" tygon clear fuel hose and the stuff holds up for about 3 years.
cost me like 15.00
The brand I used is Oregon, it is a Tygon fuel hose.
Tygothane (Saint Gobain is the Manufacturer)
U.S. Plastics is the retailer.
TygonŽ Tubing Category | Tygon, Tygon Tube and Tygon Lab Tubing. | U.S. Plastic Corp.
More Notes: Authousaz has this info next to the Fuel Return Line: Fuel Hose/Line; 3.2mm ID x 1.9mm;
According to this site: Convert inches to mm - Conversion of Measurement Units
1/8"= 0.125"=3.175mm
So 1/8" ID Hose is actually a little tighter than the 3.5mm stock Hose.
Also for the Fuel Return Lines Mercedes and the VW Dealer sell it in 1 meter legths and if you are careful cutting 1 meter is enough for a 5 Cylinder. In fact 1 meter was enough for My 6 cylinder Volvo